One problem is that conventional electric switching devices with electrical contacts in oil have a low contact opening speed. This is due, inter alia, to the fact that in connection with contact opening, hydraulic counter forces arise in the oil, which together with the other forces of inertia provide a relatively low initial contact opening speed.
Problems with welding arcs and other arcs in connection with contact opening also arise. In connection with reactive power compensation with the aid of thyristors, it is desirable that a sufficiently high voltage is built up across the contact point for the thyristors to be able to fire. To make possible a considerable operating endurance, it is important that moderate welding arcs or other arcs arise since otherwise these will rapidly erode the contact surfaces.
Modern circuit breakers, because of the current and voltage range in which they are operating, of necessity have large dimensions, which requires a relatively high operating energy which, in turn, limits the speed of action.
For use in applications mentioned under the heading "technical field" above, the available circuit breakers are overdimensioned primarily from the point of view of voltage. The SF.sub.6 circuit breaker is the breaker which most closely corresponds to the present invention. The SF.sub.6 circuit breaker is designed to manage voltages approximately 10 times higher than what is necessary for these applications. Characteristic data for the SF.sub.6 circuit breaker show that it can be operated up to 150 times at 10 kA and if the current increases to 60 kA, it manages about 15 operations. The problems with welding and other arcs are here overcome by the SF.sub.6 gas blowing out the arc arising upon contact opening. As will be clear from the stated data, the operating endurance is not very high, nor is the operating speed.
Other circuits breakers available are vacuum circuit breakers and oil-minimum circuit breakers. However, for the intended applications of the electric switching device, neither the operating endurance, nor the operating speed of these breakers is sufficient, while at the same time their required operating energies are too large.